Attenuator vs. post-phase inverter MV...

[Jack Gilvey]

I forget the forum, but I read somewhere that most of the "sound" of a cranked tube amp comes not so much from power-tube distortion (which is rare) but from overdriving the phase inverter. That being the case, a Master Volume placed after the phase-inverter will achieve much the same tone as an attenuator. Thoughts?

[Kap'n]

Post-PI master volumes simply sound different than an attenuator. Some, but not all of output stage distortion can be attributed to the PI. If that was true, somebody would have already made hybrid amps to capitalize on it. AFAIK, nobody has.

One of the things that happens with a Post-PI MV is that it's inside the negative feedback loop. Funny things happen. To my ear, an amp distorts earlier on the preamp volume when the master is turned down.

[Jack Gilvey]

Post-PI master volumes simply sound different than an attenuator. Some, but not all of output stage distortion can be attributed to the PI. If that was true, somebody would have already made hybrid amps to capitalize on it. AFAIK, nobody has.

Noted. As I recall, the person also offers mods on amps which involve adding a MV after the PI...

One of the things that happens with a Post-PI MV is that it's inside the negative feedback loop. Funny things happen. To my ear, an amp distorts earlier on the preamp volume when the master is turned down.

Hmm...any guess as to why?

[Kap'n]

Hmm...any guess as to why?

Not really, I'm just a hack.

Maybe it's due to the tubescreamer effect, a nifty phrase I invented about a second ago.

In a tube screamer, rather than distorting a signal directly, the signal in the negative feedback loop is distorted. The amplifier uses the -fb loop as a reference point, of sorts, and tries to "correct" the normal signal to the distorted sound.

Maybe a PPIMV has a similar effect?

I dunno. I'm making this up as I go along. YMMV, etc.

[Jack Gilvey]

Not really, I'm just a hack.

I dunno, bro'. Your intuitive understanding allows you to present information in such a way that someone with no background can have a clue. For the reader, this is preferable to being able to reel off techno-babble in order to show how much you know.